The invention pertains to a device for gathering printed sheets, particularly signatures and/or individual sheets.
During the gathering process in a book binding system, an individual signature is respectively withdrawn from several collections of identical signatures, wherein the various decollated signatures are delivered to a collecting conveyor in order to form stacks.
A gathering machine with feed stations according to the longitudinal withdrawal principle is known from DE 196 16 047 A1, wherein this gathering machine comprises a conveyor belt that carries a signature stack in a magazine such that a region of the folded edge remains exposed and respectively advances the bottom signature in a correspondingly cyclic fashion, as well as a withdrawal conveyor system that serves for receiving and additionally transporting the advanced signatures and is composed of acceleration rollers. Before the advance, the bottom signature is taken hold of by a suction element in the exposed region of the folded edge and tilted away from the signature stack. Blast air nozzles generate an air cushion between the tilted signature and the following signature. A clamping conveyor consisting of an upper and a lower conveyor belt is arranged downstream of the withdrawal conveyor system and inclined toward the collecting conveyor, wherein this clamping conveyor deposits the decollated signatures on the stack being formed with a synchronous transport movement upstream of a pusher of the collecting conveyor. The signatures decollated by the feeder stations are delivered to the collecting conveyor without a change of direction.
Another decollating device for feeding sheets in the longitudinal direction is known from EP 1 520 817 A1. The separating device for lifting the exposed edge region of the bottom signature off the signature stack and the transport element for delivering the signature are arranged in a combined fashion on a withdrawal unit. This withdrawal unit features a feed surface that extends along the exposed edge region and is provided with suction openings, wherein this feed surface lifts the exposed edge region off the signature stack by means of a rotational movement due to its rolling contact with the respective signature. Before the withdrawal unit feeds the signature to an additional conveyor for delivering the signature to the collecting conveyor in the form of a transport movement perpendicular to the separating movement, the edge region is fixed on the feed surface with the aid of pressing elements. The withdrawal unit with the magazine arranged thereon and the additional conveyor are arranged in a straight line and inclined toward the collecting conveyor in the transport direction such that the signature transported over the magazine bottom is delivered to the collecting conveyor in a straight fashion.
One disadvantage of these known decollating devices can be seen in that head-folded signatures cannot be decollated if they are stacked in the magazine such that the head side points rearward. The separating elements are unable to collectively lift the at least two sheet sections of the signature off the signature stack in the front region of the magazine such that an upper sheet section is held back on the retaining element of the magazine and the signature cannot be pushed out. The known decollating devices feature a plurality of successively arranged transport devices, wherein a few of these transport devices carry out intermittent or pendulum-type movements and therefore have a complicated design. The gathering capacity of known decollating devices is limited due to the fact that an ensuing decollating process can only be initiated once the preceding signature is completely withdrawn from the magazine.